The invention relates to a method for recycling polyesters or polyester mixtures from polyester-containing waste, in which the polyester or the polyester mixture are dissolved in a solvent and subsequently free-flowing particles are precipitated herefrom with a precipitant. The precipitant is thereby chosen such that subsequent separation of precipitant and solvent is made possible in a simple manner.
With increasing use of polyethylene terephthalate (PET) packaging applications, in particular in film and bottle applications, ever greater quantities of polluted highly-coloured PET waste occur, which must be disposed of or recycled.
Colourless transparent PET materials, for example returnable and non-returnable applications for mineral water or soft drinks, can be reprocessed by means of conventional material recycling methods (comminution, washing, vacuum-drying, if necessary solid phase post-condensation) in such a manner that even re-use is possible. In problematic applications, such as food packaging, there is no process for mixed coloured and partially opaquely pigmented post-consumer PET waste (including blends and composites) which makes PET re-use as food packaging technically possible.
In addition to the conventional material recycling methods, solvent-based methods have been developed in the last few years for PET in addition to known solvolysis methods (degradation of the polyester into monomer units), J. G. Poulakis, C. D. Papaspyrides: Dissolution/Reprecipitation: A Model Process for PET Bottle Recycling, Journal of Applied Polymer Science, Vol. 81, 91-95 (2001), EP 0 850 982, DE 100 177 07, U.S. Pat. No. 5,866,622. At least the last-mentioned method represents a partial solvolysis due to the unavoidable molar mass degradation there.
A method is known from EP 0 742 251 for reclaiming polyester polymer from a mixed polymer recycling flow, which comprises bringing the polymer mixture into contact with a chemical washing solvent and separating the contaminated chemical washing solvent resulting therefrom from the remaining mixed polymer recycling flow, bringing the remaining mixed polymer recycling flow into contact with a further polyester-dissolving solvent, separating the polyester-containing selective solvent from the non-dissolved residue and separating the thus obtained polyester. When using the chemical washing solvent described here, the problem occurs here however that the partial dissolution of the PET cannot be prevented.
Conventional material recycling methods just like the existing solvent-based methods involve the disadvantage that only inadequate separation of foreign polymers and other undesired disruptive materials, such as e.g. degradation products, additives, fillers or filler residues is possible. Hence high-quality material recovery of PET waste from mixed waste (so-called post-consumer collections) is prevented.
A further disadvantage is based on the fact that the methods known from the state of the art require thermal processing of the solvent and precipitant which are used. This is connected consequently to a high energy requirement for this method.